1. Field of the Invention
The present invention relates to a white light source and a display apparatus using the white light source. Specifically, it relates to a high-quality white light source that is suitable as a light source of display apparatus and to a display apparatus using the white light source.
2. Description of the Related Art
Liquid crystal displays comprising liquid crystals as display panels have practically been used as display apparatus. Such liquid crystal displays essentially require light sources (back-lights) to display color images on the liquid crystals.
Demands have recently been made on further miniaturized and higher-quality light sources. To improve image quality of such liquid displays as display apparatus, white light emitted from the light sources must have further improved quality. To improve image quality and to increase luminance, the light sources must have optimized white-light temperature, improved luminance saturation, luminance degradation and decay characteristics.
One of these white light sources is a light source comprising a phosphor screen and an ultraviolet-visible light emitting lamp such as a blue light emitting diode (blue-LED) that is capable of exciting a phosphor screen and allowing the same to emit a first visible light component and is capable of emitting a second visible light component. This light source yields white light by mixing these visible light components.
The luminance saturation and luminance degradation of the light sources using phosphor screen significantly vary depending on the type, production method, dopants (impurities) and composition of phosphor materials. To improve these characteristics, a phosphor having improved characteristics has been selected or the composition and production method of such a phosphor have been improved. However, no conventional single phosphor material has sufficiently satisfied all the required characteristics.
To reduce the aforementioned disadvantages, a Y3(Al,Ga)5O12:Ce phosphor exhibiting less luminance degradation has been used. This phosphor emits yellowish green light and yields white light by mixing the green light with a blue light component emitted from an excitation light source for allowing the phosphor to emit light. However, this phosphor cannot yield a sufficient color temperature.
Accordingly, the phosphor has deteriorated reproducibility as a phosphor for white light sources and cannot be used alone as a phosphor in display apparatus (see, for example, Japanese Published
Accordingly, an object of the present invention is to solve the above problems and to provide a high-quality white light source capable of emitting an increased red light component in addition to luminous colors of the conventional Y3(Al,Ga)5O12: Ce green light phosphor used in such light sources, as well as to provide a display apparatus using the white light source.
To achieve the above and other objects, the present invention provides, in an aspect, a white light source including an ultraviolet-visible excitation light generation unit capable of generating ultraviolet light and first visible light of wavelength of from 400 nm to 500 nm, and a fluorescence generation unit having a phosphor layer and being capable of generating second visible light upon irradiation of ultraviolet-visible light generated from the ultraviolet-visible excitation light generation unit as excitation light. The white light source yields white light by mixing the first visible light from the ultraviolet-visible excitation light generation unit and the second visible light from the fluorescence generation unit. In the white light source, the phosphor layer includes a red light emitting phosphor represented by following Compositional Formula (1):
xe2x80x83(Ca1xe2x88x92axe2x88x92bSraEub)S:Mcxe2x80x83xe2x80x83(1)
wherein a, b and c satisfy the following conditions:
0xe2x89xa6a less than 1.0, 0 less than bxe2x89xa60.1 and 0xe2x89xa6cxe2x89xa60.1; 
and M is a dopant element having an absorption of excitation energy in a range from about 350 nm to about 500 nm. The element M may be at least one rare earth element selected from Ce, Yb, Gd and Tm.
Part of Ca and/or Sr in Compositional Formula (1) may be substituted by Zn. In this case, the red light emitting phosphor is represented by following Compositional Formula (2):
(Ca1xe2x88x92axe2x88x92bxe2x88x92dSraZndEub)S:Mcxe2x80x83xe2x80x83(2) 
wherein a, b, c and M are as defined above; and d satisfies the following condition: 0.01xe2x89xa6dxe2x89xa60.1.
The phosphor layer of the fluorescence generation unit may further include a magnesium fluorogermanate phosphor in addition to the red light emitting phosphor represented by Compositional Formula (1) or (2).
The phosphor layer of the fluorescence generation unit may further include a green light emitting phosphor represented by following Compositional Formula (3):
(Y1xe2x88x92axe2x88x92bGdaCeb)3(Al1xe2x88x92cGac)5O12xe2x80x83xe2x80x83(3) 
wherein a, b and c satisfy the following conditions: 0xe2x89xa6axe2x89xa61.0, 0 less than bxe2x89xa60.1 and 0xe2x89xa6cxe2x89xa61.0, in addition to the red light emitting phosphor represented by Compositional Formula (1) or (2). The content of the green light emitting phosphor is preferably from about 40% to about 80% by weight based on the total weight of phosphors constituting the phosphor layer.
The phosphor represented by Compositional Formula (3) preferably further includes K (potassium) as a dopant (an impurity). The green light emitting phosphor in this case is represented by following Compositional Formula (4):
(Y1xe2x88x92axe2x88x92bGdaCeb)3(Al1xe2x88x92cGac)5O12:Kdxe2x80x83xe2x80x83(4) 
wherein a, b and c satisfy the following conditions: 0xe2x89xa6axe2x89xa61.0, 0 less than bxe2x89xa60.1 and 0xe2x89xa6cxe2x89xa61.0; K is contained as a dopant; and d is ppm by weight and satisfies the following condition: 0xe2x89xa6dxe2x89xa61000
The content of the green light emitting phosphor represented by Compositional Formula (4) is preferably from about 40% to about 80% by weight based on the total weight of phosphors constituting the phosphor layer.
The monovalent metal element M as a dopant can be introduced into the phosphor represented by Compositional Formula (1) or (2) by adding a predetermined amount of a sulfate or borate of M, such as potassium sulfate or sodium borate, as a flux to the phosphor upon synthesis thereof. Among these fluxes, potassium sulfate is typically preferred.
In the green light emitting phosphor represented by Compositional Formula (3) or (4), the ratio of the X-ray diffraction peak intensity of GdAlO3 in the (211) orientation to that of the green light emitting phosphor represented by Compositional Formula (3) or (4) in the (420) orientation may be less than or equal to one fifth in the determination of X-ray diffraction peak intensity using Kxcex1 characteristic X-ray of Cu.
The ultraviolet-visible excitation light generation unit of the light source includes, for example, an excitation light source that emits a visible light component and an ultraviolet light component, such as an ultraviolet light lamp, blue-flourescent lamp or a gallium nitride (GaN) blue light emitting diode (hereinafter briefly referred to as xe2x80x9cblue-LEDxe2x80x9d) having a luminous peak in a range from about 350 nm to about 460 nm. The phosphor layer constituting the fluorescence generation unit is preferably formed so as to cover at least a light emitting surface of the excitation light source.
In another aspect, the present invention provides a display apparatus having a light source. The light source includes a fluorescence generation unit having a phosphor layer and being capable of generating visible light, and an excitation light generation unit capable of irradiating the phosphor layer with excitation light and allowing the phosphor layer to generate visible light, in which the light source is the white light source of the present invention.
One of the features of the display apparatus of the present invention is the aforementioned white light source. Preferred configurational embodiments of the display apparatus will be illustrated below.
Specifically, the display apparatus preferably includes a display panel, the light source and a control device capable of controlling visible light irradiated by the light source to thereby display an image on the display panel, in which the light source has a control device capable of controlling change in emission intensity of one of red, green and blue light with time to thereby control changes in emission intensities of the red, green and blue light with time.
In the display apparatus just mentioned above, the white light source further preferably has a control device capable of controlling a change in emission intensity of the blue light emission of the blue-light discharge lamp constituting the excitation light generation unit of the white light source to thereby control changes in emission intensities of red, green and blue light with time.
The display apparatus of the present invention is preferably applied to a display apparatus including a liquid crystal display panel. In this case, the display apparatus includes a liquid crystal display panel, a light source constituting a back-light of the liquid crystal display panel, and a control device allowing the liquid crystal display panel to display image information. In this display apparatus, the light source constituting the back-light includes the white light source of the present invention.
The display apparatus may include a fluorescence generation unit having a phosphor layer and being capable of generating visible light, and an excitation light generation unit capable of irradiating the phosphor layer with excitation light and allowing the phosphor layer to emit light, in which the phosphor layer includes a mixture of any materials of the red light emitting phosphor and the green light emitting phosphor.
In addition, the present invention provides a display apparatus including a fluorescence generation unit having a phosphor layer and being capable of generating visible light, and an excitation light generation unit capable of irradiating the phosphor layer with excitation light and allowing the phosphor layer to emit light, in which the excitation light generation unit includes a blue light emitting discharge lamp as an excitation light source, and the fluorescence generation unit has a phosphor layer including the red light emitting phosphor layer and a green light emitting phosphor layer separately disposed adjacent to each other.